I always loved the way that Apple handled the virtual desktop interface, and even though they simplified the usage in the latest version of Mac OS X it still has some of the intuitive drag-and-drop ease that Spaces offered on past versions of the OS. One of the most popular virtual desktop solutions for Windows, called Dexpot, has a Beta version of their app that works in a similar way.
Dexpot 1.6 Beta will let you tile all of the virtual desktops as pictured above, and you can grab any of the windows from one desktop and drop them in another. By default the windows of each desktop aren’t tiled so you may not see some of the background windows, but right-clicking on one of the desktops will tile the apps on that desktop so that you can clearly see everything. If you right-click in the black space separating any of the virtual desktops that will cause all of them to tile their apps. To activate this view you’ll need to switch to the “Full-Screen Preview” which is available through the System Tray icon or by using the WinKey+F3 keyboard shortcut, which can be customized in the settings.
Check out this page to see everything that’s new in Dexpot 1.6 Beta (including multi-monitor support) and to download the pre-release version.
Dexpot Homepage (Windows only; Free for Personal Use)